JPS5840719B2 - Cleaning equipment for nuclear fuel bodies in use at nuclear reactor facilities - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a cleaning device for cleaning nuclear fuel assemblies in use in a nuclear reactor, and particularly to a cleaning device for nuclear fuel assemblies in use that is suitable for a boiling water light water reactor.

It is known that impurities carried by light water, which is a coolant, adhere to the outer circumferential surface of a nuclear fuel assembly that constitutes the core of a boiling water reactor.

Adhesion of a large amount of impurities on the outer circumferential surface of the nuclear fuel assembly reduces the heat transfer efficiency of the nuclear fuel assembly, resulting in damage to the cladding tube of the nuclear fuel assembly due to corrosion.

In addition, even in the case of adhesion of impurities in amounts that do not cause damage to the cladding, these adhering impurities become radioactive during reactor operation, peel off and are sent to the primary system piping along with the coolant, and are deposited on the piping surface. As a result, the radiation dose on the surface of the secondary system piping increases.

Therefore, it is necessary to remove impurities adhering to the outer peripheral surface of the nuclear fuel assembly, and it is necessary to clean the fuel assembly when the reactor is shut down.

In principle, chemical cleaning methods and physical cleaning methods can be considered as methods for cleaning fuel bodies, but chemical cleaning methods have the following problems and cannot be adopted as a method for cleaning nuclear fuel bodies.

In other words, when a chemical cleaning method is adopted as a nuclear fuel assembly cleaning method, chemicals may adhere to the outer surface of the nuclear fuel assembly after use, or several ppd may be present in the reactor water due to diffusion into the reactor water.
It is unavoidable that some concentrations remain.

This residual chemical is expected to become activated when the reactor restarts, causing corrosion, stress corrosion cracking, and other adverse effects on the reactor core and other parts, which is extremely dangerous.

On the other hand, when adopting a physical cleaning method, the sponge pole cleaning method, which has been used in the past for cleaning condenser piping in thermal power plants, is considered to be effective; The flow path between the nuclear fuel rods is extremely narrow compared to the inner diameter of the piping, and it also contains minute structures such as spacers, so there is a risk that the sponge poles will become clogged and block the flow path.

However, the physical cleaning method is considered to be more effective as a method for cleaning nuclear fuel bodies than the chemical cleaning method because it is thought that there is less concern about adverse effects on the equipment after cleaning as in the case of the chemical cleaning method.

Therefore, in order to avoid blockage of the flow path in the nuclear fuel by solid particles, easily meltable solid particles such as ice or low melting point paraffin, which can be melted at a certain temperature or higher, are used as solid particles.
It has been considered in the past that physical cleaning methods can be used effectively to eliminate defects by preventing solid particles from clogging pipes. However, it requires a complex configuration and equipment.

Furthermore, the post-treatment of solid substances may not be sufficient, resulting in insufficient cleaning effects.

SUMMARY OF THE INVENTION An object of the present invention is to provide a cleaning device for a nuclear fuel assembly in use in a nuclear reactor facility, which has a reliable radiation shielding effect in a cleaning section and has high cleaning efficiency.

The present invention is characterized in that it is a cleaning device for cleaning a nuclear fuel assembly in use in a nuclear reactor facility having a fuel exchange pool in which a reactor pressure vessel is immersed, a storage pool for storing nuclear fuel before use, etc. A cleaning tank submerged in pool water of a replacement pool or a storage pool and isolated from the pool water, and a cleaning liquid supply device connected to the cleaning tank and allowing cleaning liquid to penetrate into the cleaning tank, the cleaning liquid supply device The device comprises a pump, a supply device for temperature-melting solid substances, and a waste separator.

Embodiments of the present invention will be described below with reference to the accompanying drawings.

First, a first embodiment of the present invention will be described with reference to FIGS. 1 and 2.

FIG. 1 shows the configuration of an apparatus for carrying out the cleaning method of the present invention, and shows an example in which the present invention is applied to a boiling light water reactor facility.

In FIG. 1, 1 is a reactor pressure vessel, and the reactor pressure vessel 1 is submerged in water of a fuel exchange pool 2 in a reactor containment facility.

Inside the reactor pressure vessel 1 are a reactor core 3 composed of a large number of nuclear fuel assemblies, a shroud 4 disposed surrounding the reactor core 3, and an upper plenum and a lower plenub disposed around the shroud 4. several jet pumps that communicate
and are accommodated.

Figure 1 shows the state in which the lid of the reactor pressure vessel 1 has been removed for cleaning the nuclear fuel assembly, so that the reactor water in the pressure vessel 1 and the pool water in the fuel exchange pool 2 are separated. are mixed.

A cleaning tank 6 isolated from the pool water is submerged in the pool water of the fuel exchange pool 2.

This cleaning tank 6 is, for example, a cylindrical airtight container 0, and the pipe line p
1. It is connected to the cleaning liquid supply device 7 on the ground via p2.

FIG. 2 shows the detailed structure of the cleaning tank 6 in which the nuclear fuel assembly 30 is accommodated.

As shown in FIG. 2, the cleaning tank 6 has a lid 61 and a main body 62.
Tokara.

The lid 61 and the main body 62 each have a double wall structure, with respective outer peripheral walls 61A and 62A and respective inner peripheral walls 61B.
, 62B is kept in a vacuum.

A heat insulating material 61 is provided on each inner peripheral wall of the lid 61 and the main body 62.
C, 62C is coated, thereby further enhancing the heat insulating effect of the tank 6.

At each end of the lid 61 and the main body 62, there is a conduit P1. P
Connecting pipes 61D and 62D connected to the cleaning tank 6 are attached, and these connecting pipes 61D and 62D open into the internal space of the cleaning tank 6.

A ring-shaped flange 62E having a center hole that opens conically upward is attached to the lower inner circumferential surface of the main body 62, and this flange 62E is attached to the nuclear fuel assembly 3 as shown in FIG.
0 serves as a seat that engages with the outer peripheral surface of the lower clamp plate 30D of the nuclear fuel assembly 30 when inserted into the main body 62.

Another flange 62F is provided on the inner peripheral surface of the upper end of the main body 62.
is attached, and the inner peripheral inclined surface a of this flange 62F serves as a guide when inserting the nuclear fuel assembly 30 into the main body 62. do.

), as is well known, includes a large number of fuel rods 30A arranged in parallel, a channel box 30B surrounding the fuel rods 30A, and a channel box 30B.
The upper and lower ends of the fuel rod 30C and the lower end of the fuel rod 30A are fixed to each other.

On the other hand, a flat ring-shaped flange 61E is fixed to the inner circumferential surface of the lid 61 of the cleaning tank 6, as shown in FIG. A movable flange 61G is suspended.

The movable flange 61G has an inclined portion extending downward and outward at its outer peripheral edge, and a flexible material 61H such as rubber is attached to the lower surface of the flange 61G.

This flexible material 61H engages with the upper end of the channel box 30B of the nuclear fuel assembly 30 when the nuclear fuel assembly 30 to be cleaned is sealed in the cleaning tank body 62, and securely holds the nuclear fuel assembly 30 in the cleaning tank 6. It is for the purpose of

An outer periphery flange 61J protrudes from the outer periphery of the respective mating surfaces of the frame 61 and the main body 62.

62G, and the lid 61 and main body 62 are integrated through these flanges 61G and 62G.

A conical surface for guiding the outer circumferential flange 61J of the lid 61 is formed on the upper surface of the outer circumferential flange 62G formed on the main body 62.

A latch or latch 62H made of an elastic material such as a plate is also attached to the outer peripheral flange 62G of the main body 62, and the tip of this latch 62H is strongly engaged with the upper surface of the outer peripheral flange 61J of the lid 61. It is.

Note that the symbol R in FIG. 2 is an O-ring, and the O-ring R provided on the inner peripheral surface of the flange 62E is used to prevent cleaning liquid from flowing into the channel box 3 of the nuclear fuel assembly 30 during cleaning.
This is to prevent the water from flowing along the outer periphery of 0B.

Next, referring again to FIG. 1, the configuration of the cleaning liquid supply device 7 included in a part of the apparatus of the present invention will be explained.

The cleaning liquid supply device 7 is installed on the ground in the reactor containment facility, and the device 7 includes a cleaning liquid tank 71, a filth separator 72, a pump 73, a soluble solid material supply device 74, and a shape sorter 7.
5 and a mixer 76, and the pipes P1 to P3 connecting these components are equipped with valves 1. ■2. ■3. ■4 is provided.

The cleaning liquid stored in the cleaning liquid tank 71 may be water if the nuclear reactor is a light water reactor.

A waste separator 72 installed downstream of the cleaning liquid tank 71
is for removing dirt from the cleaning liquid returned from the cleaning tank 6 through the pipe P2, and various types of filters can be used.

As mentioned above, the meltable solid substance mixed into the cleaning liquid is ice, paraffin, etc. When ice is used, a refrigerant coil 77 is installed in the cleaning tank 71 to keep the temperature of the cleaning liquid low. good.

The shape sorter 75 removes meltable solid substances of a certain size or more, and a sieve or the like may be used.

Next, the use of the apparatus of the present invention will be explained with reference to FIGS. 1 and 2.

The reactor operation was stopped for cleaning the nuclear fuel body, and several days after the core temperature became low, the lid (not shown) of the reactor pressure vessel 1 was opened, and the reactor water in the pressure vessel 1 was transferred to the fuel exchange pool 2.
The refueling pool 2 is filled with reactor water.

One nuclear fuel assembly 30 is pulled out from the reactor core 3 into the pool 2 using an existing crane (not shown), and at the same time, the lid 61 of the cleaning tank 6 is opened and the nuclear fuel assembly 30 is pulled out into the main body 62 of the cleaning tank 6. suspended inside.

In this case, the surface a of the inner peripheral flange 62F of the cleaning tank 6 guides the lower tie brake 30D of the nuclear fuel assembly 30, so that the axial center of the nuclear fuel assembly 30 and the axial center of the cleaning tank 6 naturally coincide.

After the nuclear fuel assembly 30 has been suspended into the cleaning tank main body 62, the lid 61 is suspended onto the main body 62, and as a result, the lid 61 is suspended above the outer peripheral flange 62G of the main body 62, as shown in FIG. , and both are clamped by the launch 62H.

When the lid 61 is suspended, the outer periphery flange 62G of the main body 62
The inclined surface acts as a guide for the lid 61 and facilitates positioning of the lid 61.

When the lid 61 is closed, the movable flange 6 inside the lid 61
1G is elastically pressed against the upper end of the channel box 30B of the nuclear fuel body 30 via the flexible material 61H, and
0 is held in the cleaning tank 6 so as not to move.

Next, the pump 73 in the cleaning liquid supply device 7 is started, and at the same time valves 1 to 4 are opened, and the cleaning liquid is pumped into the cleaning tank 6 through the pipe P1.

Small pieces of ice or small pieces of low-melting paraffin are mixed into the cleaning liquid by a mixer 76 at a predetermined mixing ratio.

The cleaning liquid pumped into the cleaning tank 6 ascends from the bottom of the cleaning tank 6 through the flow path between the fuel rods 30A of the nuclear fuel assembly 30 as shown by the arrow in FIG. The deposits are rubbed off by friction with solid substances in the cleaning solution.

While flowing through the nuclear fuel assembly, the solid substances in the cleaning liquid gradually melt due to friction with the circumferential surface of the fuel rods and decay heat generated from the fuel rods, and when they return to the cleaning liquid tank 71 through the pipe P2, most of the solid substances are melted. melts.

The cleaning liquid that has returned to the cleaning liquid tank 71 is sent to a dirt separator 72 to remove deposits from the nuclear fuel assembly, and then to a mixer 76 where meltable solid substances are mixed therein.

After the cleaning is completed, the cleaning liquid supply device 7 is operated for several more minutes.
The cleaning liquid contained in the pipes P1 and P2 is purified.

After that, the pump 73 is stopped and the valves (1) to (v4) are closed, and then the lid 61 of the cleaning tank 6 is opened and the nuclear fuel assembly 30 is drawn out from inside the cleaning tank 6.

In the first embodiment shown in FIG. 1, the cleaning liquid always flows through the cleaning tank 6 in one direction, but this method of always causing the cleaning liquid to flow in only one direction is not suitable for cleaning liquid. It has been found that the cleaning effect is inferior to methods in which the flow direction is alternately switched.

According to experiments, when a nuclear fuel assembly is cleaned using the method of the first embodiment, the parts that come into contact with the cleaning liquid first are cleaned best;
It was found that the cleaning effect on the downstream side was reduced.

Therefore, by alternately reversing the flow direction of the cleaning solution, it was found that the same cleaning effect could be obtained by mixing half the amount of solid substances into the cleaning solution compared to a unidirectional flow cleaning method. .

FIG. 4 is a diagram illustrating this fact.

In FIG. 4, the horizontal axis shows the length from the bottom end to the top end of the nuclear fuel body, and the vertical axis shows the cleaning effect.

In Fig. 4, the broken line (■) shows the cleaning effect over the entire length of the nuclear fuel assembly when cleaning is performed by a cleaning method in which the cleaning liquid flows from the lower end to the upper end of the nuclear fuel assembly.
From this curve (2), it can be seen that in cleaning by such a one-way flow-through method, the cleaning effect is greatest at the lower end of the nuclear fuel assembly, and the cleaning effect rapidly decreases at the upper end of the nuclear fuel assembly.

The reason for this is that the meltable substances mixed in the cleaning fluid are partially melted or are reduced in friction while flowing through the nuclear fuel assembly due to the decay heat generated from the nuclear fuel assembly.

Curve shown in Figure 4 ■ (Curve shown as a dashed-dotted line)
shows the cleaning effect when the amount of meltable substances in the cleaning fluid is halved, the cleaning time is also halved, and the cleaning fluid flows from the lower end of the nuclear fuel assembly to the upper end compared to the case shown by curve ■. It shows.

Similarly, the curve ■ shown by the two-dot chain line has the amount of meltable substances in the cleaning liquid and the cleaning time halved compared to the case shown by the curve ■, and the cleaning liquid flows from the upper end to the lower end of the nuclear fuel body. This shows the cleaning effect when flowing through in one direction.

From these curves (1) and (2), it can be seen that when cleaning is performed by the unidirectional flow-through method, the portion that comes into contact with the cleaning group first is cleaned best.

Curve ■ (solid curve) is a curve that shows the composite value of curves ■ and ■.As can be seen from this curve, if the flow direction of the cleaning fluid is alternately switched, the cleaning effect will be increased over the entire length of the nuclear fuel assembly. It can be inferred that the imbalance can be reduced.

FIG. 3 shows a second embodiment constructed based on this result.

(In FIG. 3, the same parts as those shown in FIG. 1 are indicated by the same reference numerals.

) In the embodiment shown in FIG. 3, in the cleaning liquid supply device 7 of FIG. 1, the pipe P1. Pipe P3 connected between P2
, P4 are provided, and a valve ■5 is provided in the pipe P3.
Further, a feature is that each of the pipes P4 is provided with a valve (6).

Valve (2) and valve (2) 6 are closed when the cleaning liquid is forced into the cleaning tank 6 from the pipe P1, and are opened when the cleaning liquid is forced into the cleaning tank 6 from the pipe P2.

Therefore, according to the arrangement shown in FIG. 3, the flow direction of the cleaning liquid flowing through the cleaning tank 6 is alternately switched, so that the cleaning effect is improved compared to the device shown in FIG. The amount of solid material can be reduced.

Figure 5 shows the amount of radioactive material (e.g. cobalt-60) deposited on the nuclear fuel assembly when the reactor continues to operate without cleaning the nuclear fuel assembly, and the amount of radioactive material on the nuclear fuel assembly when the nuclear fuel assembly is cleaned. Curve A shown as a solid line shows the change in the amount of radioactive material adhered when not cleaned, and curve B shown as a broken line shows the change in the amount of radioactive material adhered when cleaning is done every year. Shows changes in adhesion amount.

From this diagram, it can be seen that by cleaning the nuclear fuel assembly every year, the amount of radioactive deposits will vary greatly in just a few years.

Therefore, by applying the present invention to, for example, a nuclear power plant, the safety of the nuclear power plant can be greatly improved.

Although a closed container is used as the cleaning tank in the embodiment, it does not necessarily have to be a closed container, and for example, a part of the fuel exchange pool 2 can be used in isolation.

As described above, according to the present invention, the nuclear fuel to be cleaned can be brought into and out of the cleaning tank while submerged in the pool water, and contact with the gas phase can be completely cut off. Prevention can be achieved reliably and easily without particularly requiring a shielding wall or the like.

Furthermore, by having the cleaning tank and pressure vessel coexist in the pool water, the nuclear fuel extracted from the reactor core can be immediately stored in the cleaning tank and cleaned by contacting it with cleaning liquid mixed with temperature-melting solid substances. Therefore, by maintaining the exothermic state based on the decay heat of the radioactive material during combustion and performing the cleaning action, the solid substances in the cleaning liquid that returns to the cleaning liquid supply section can be removed without the need to prepare a special heat source for melting the solid substances. Melting can be performed.

Therefore, it is easy to separate the deposits, and when the cleaning liquid is recirculated to the cleaning tank, the used solid material can be easily removed, and the new solid material can efficiently remove the deposits. effect is produced.

[Brief explanation of drawings]

FIG. 1 is an overall configuration diagram showing the first embodiment of the present invention.
The figure is an enlarged vertical sectional view of a part of the part shown in Figure 1,
The figure shows the second embodiment of the present invention, Figure 4 shows the flow direction of the cleaning group and lines showing the cleaning effect, and Figure 5 shows radioactive deposits on the nuclear fuel body with and without cleaning. FIG. 3 is a diagram showing a comparison of adhesion amounts. Explanation of symbols, 1... Reactor pressure vessel, 2...
...Fuel exchange pool, 6...Cleaning tank, 7.
...Cleaning liquid supply unit.

Claims (1)

[Scope of Claims] 1. A cleaning device for cleaning a nuclear fuel assembly in use in a nuclear reactor facility having a fuel exchange pool in which a reactor pressure vessel is immersed, a storage pool for storing nuclear fuel before use, etc. A cleaning tank submerged in pool water of the fuel exchange pool or storage pool and isolated from the pool water, and a cleaning liquid supply device connected to the cleaning tank and causing a cleaning group to flow through the cleaning tank, The cleaning liquid supply device is a cleaning device for a nuclear fuel assembly in use in a nuclear reactor facility, and includes a pump, a temperature-melting solid material supply device, and a waste separator. 2. In the cleaning device according to claim 1, the cleaning liquid supply device is provided with a switching valve that can change the flow direction of the cleaning liquid in the cleaning tank to either forward or reverse direction. A cleaning device for nuclear fuel bodies in use in a nuclear reactor facility, characterized by: 3 In the cleaning device according to claim 1, the cleaning tank has a flow path that allows the cleaning fluid to contact and flow through the combustion rods of the nuclear fuel assembly, and the filth separator of the cleaning fluid supply device stores the cleaning fluid that is recycled. A supply device for temperature-melting solid substances is connected to the downstream side of the tank and is connected to a mixer via a shape sorter, and this mixer is connected to the downstream side of the waste separator to remove the solid substance-containing cleaning liquid. A cleaning device for nuclear fuel assemblies in use in a nuclear reactor facility, characterized in that the cleaning device is configured to supply water to the cleaning device.